JP2022155737A - Micro LED display device - Google Patents

Abstract

To provide a micro LED display device with excellent luminous efficiency and suppressed color mixture.SOLUTION: A micro LED display device according to the present invention includes a micro LED array substrate including a plurality of micro LEDs, a sealing portion that seals the plurality of micro LEDs, a low refractive index layer, and a plurality of wavelength conversion layers formed by partitioning in this order from the back side, and each of the wavelength conversion layers is formed such that a pair of layers corresponds to one micro LED in a thickness direction, and the refractive index of the low refractive index layer is lower than the refractive index of the sealing portion and the refractive index of the wavelength conversion layer, and a difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is 0.10 or more, and a difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is greater than or equal to 0.10.SELECTED DRAWING: Figure 1

Description

The present invention relates to micro LED display devices.

In recent years, as a new display device, a micro LED display configured by arranging micro LEDs in pixels arranged in a matrix has been developed (for example, Patent Documents 1 and 2). The micro LED display includes a micro LED array substrate configured by arranging a plurality of micro LEDs, and a micro LED array substrate provided on the micro LED array substrate, which absorbs light from the micro LEDs and changes the emission wavelength of the light to red, A display provided with an array of wavelength conversion layers (fluorescence emission layers) that convert wavelengths of green light and blue light, respectively, has been proposed (for example, Patent Document 2). In such a micro LED display, a micro LED and a wavelength conversion layer are paired for each sub-pixel.

Japanese Patent Application Laid-Open No. 2020-43073 Japanese Patent Publication No. 2016-523450

In the micro LED display as described above, there is a problem that light from the micro LED leaks to sub-pixels (adjacent sub-pixels, peripheral sub-pixels) other than those corresponding to the micro-LED, resulting in color mixture. Moreover, there is also the problem that light returning to the back side is generated due to scattering within the wavelength conversion layer, and sufficient luminous efficiency cannot be obtained.

An object of the present invention is to provide a micro LED display device with excellent luminous efficiency and suppressed color mixture.

The micro LED display device of the present invention comprises a micro LED array substrate including a plurality of micro LEDs, a sealing portion that seals the plurality of micro LEDs, a low refractive index layer, and a plurality of wavelengths that are divided and formed. A conversion layer is provided in this order from the micro LED array substrate side, each wavelength conversion layer is formed so as to correspond to one micro LED in the thickness direction, and the low refractive index layer the refractive index is lower than the refractive index of the sealing portion and the refractive index of the wavelength conversion layer, and the difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is 0.10 or more; The difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is 0.10 or more.
In one embodiment, the low refractive index layer has a refractive index of 1.25 or less.
In one embodiment, the low refractive index layer is a void layer made of a porous body composed of chemically bonded fine particles.
In one embodiment, the sealing portion is made of an adhesive.
In one embodiment, the individual wavelength conversion layers are spaced apart by partition walls.
In one embodiment, the micro LEDs are blue LEDs or UV LEDs.
In one embodiment, the micro LED display device further comprises a color filter disposed on the side of the wavelength conversion layer opposite to the low refractive index layer.

According to the present invention, it is possible to provide a micro LED display device with excellent luminous efficiency and suppressed color mixture.

1 is a schematic cross-sectional view of a Micro LED display device according to one embodiment of the present invention; FIG. (a) is a schematic cross-sectional view showing a configuration provided for an example, and (b) is a schematic cross-sectional view showing a configuration provided for a comparative example.

A. Micro LED Display Device FIG. 1 is a schematic cross-sectional view of a Micro LED display device according to one embodiment of the present invention. The micro LED display device 100 according to the present embodiment is formed by partitioning a micro LED array substrate 10 including a plurality of micro LEDs 11, a sealing portion 20 for sealing the plurality of micro LEDs 11, and a low refractive index layer 30. and a plurality of wavelength conversion layers 40 are provided in this order from the micro LED array substrate side. Typically, the micro LED array substrate 10 includes a driving substrate 12 and a plurality of micro LEDs 11 arranged in an array (matrix) on the driving substrate 12 . Each wavelength conversion layer 40 is formed so as to correspond to one micro LED 11 in the thickness direction and form a pair. Typically, one subpixel includes one wavelength conversion layer 40 and one micro LED 11 . By transmitting the light from the micro LED 11 through the wavelength conversion layer 40, red, green, and blue sub-pixels can be formed. In addition, when the sub-pixel uses the light from the micro LED as it is (for example, when the blue sub-pixel is formed with a blue LED), the wavelength conversion layer is omitted at that location, or another layer (for example, a light diffusion layer). In one embodiment, each wavelength conversion layer is separated by partition walls 50 (light shielding layers).

In one embodiment, the low refractive index layer 30 is formed on the entire surface of the sealing portion 20 opposite to the micro LED array substrate 10 . Moreover, in one embodiment, the low refractive index layer 30 is provided directly on the sealing portion 20 (that is, without interposing another layer).

The refractive index of the low refractive index layer 30 is lower than the refractive index of the sealing portion 20 and the refractive index of the wavelength conversion layer 40 . The difference between the refractive index of the low refractive index layer 30 and the refractive index of the sealing portion 20 is 0.10 or more. Moreover, the difference between the refractive index of the low refractive index layer 30 and the refractive index of the wavelength conversion layer 40 is 0.10 or more.

In the present invention, by arranging the low refractive index layer between the sealing portion and the wavelength conversion layer, a refractive index difference occurs between the layers. As a result, at least part of the light emitted from the micro LED and scattered in the wavelength conversion layer and returning to the back side is reflected at the interface between the wavelength conversion layer and the low refractive index layer and emitted to the viewing side. can be done. As a result, luminous efficiency is improved. In addition, at least part of the light emitted from the micro LED in an oblique direction and not reaching the corresponding wavelength conversion layer (wavelength conversion layer in the same subpixel) and heading toward its periphery is the low refractive index layer and the sealing Reflected at the interface with the part and returned to the back side. As a result, color mixture is suppressed. Micro LED display devices according to embodiments of the present invention are advantageous in that, in addition to their high definition, they are also brighter and have a wider color gamut than conventional displays.

B. Low refractive index layer The refractive index of the low refractive index layer is preferably 1.30 or less, more preferably 1.25 or less, still more preferably 1.20 or less, and particularly preferably 1.15 or less. be. The lower the refractive index of the low refractive index layer, the better, but the lower limit is, for example, 1.07 or more (preferably 1.05 or more). As used herein, a refractive index refers to a refractive index measured at a wavelength of 550 nm.

As described above, the difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is 0.10 or more. The difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is preferably 0.20 or more, more preferably 0.30 or more. With such a range, the above effect becomes remarkable. The upper limit of the difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is, for example, 0.50 (preferably 0.70).

As described above, the difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is 0.10 or more. The difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is preferably 0.20 or more, more preferably 0.30 or more. With such a range, the above effect becomes remarkable. The upper limit of the difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is, for example, 0.50 (preferably 0.70).

The thickness of the low refractive index layer is preferably 0.01 μm to 1000 μm, more preferably 0.05 μm to 100 μm, still more preferably 0.1 μm to 80 μm, particularly preferably 0.3 μm to 50 μm. be.

Any appropriate configuration can be adopted for the low refractive index layer. In one embodiment, the low refractive index layer has voids. The low refractive index layer can be preferably formed by coating, printing, or the like. As materials constituting the low refractive index layer, for example, the materials described in WO 2004/113966, JP-A-2013-254183, and JP-A-2012-189802 can be employed. Specifically, for example, silica-based compounds; hydrolyzable silanes, and partial hydrolysates and dehydration condensates thereof; organic polymers; silicon compounds containing silanol groups; polymerizable monomers (e.g., (meth)acrylic monomers and styrenic monomers); curable resins (e.g., (meth)acrylic resins, fluorine-containing resins, and urethane resins); and Combinations of these are included. The low refractive index layer can be formed by coating or printing a solution or dispersion of such material.

The porosity of the low refractive index layer having voids is preferably 35% by volume or more, more preferably 38% by volume or more, and particularly preferably 40% by volume or more. Within such a range, a low refractive index layer having a particularly low refractive index can be formed. The upper limit of the porosity of the low refractive index layer is, for example, 90% by volume or less, preferably 75% by volume or less. Within such a range, a low refractive index layer having excellent strength can be formed. The porosity is a value calculated by Lorentz-Lorenz's formula from the value of the refractive index measured by an ellipsometer.

The size of the voids (pores) in the low refractive index layer refers to the major axis diameter of the major axis diameter and the minor axis diameter of the voids (pores). The size of the voids (pores) is, for example, 2 nm to 500 nm. The size of the voids (pores) is, for example, 2 nm or more, preferably 5 nm or more, more preferably 10 nm or more, and still more preferably 20 nm or more. On the other hand, the size of the voids (pores) is, for example, 500 nm or less, preferably 200 nm or less, more preferably 100 nm or less. The range of the size of the voids (pores) is, for example, 2 nm to 500 nm, preferably 5 nm to 500 nm, more preferably 10 nm to 200 nm, still more preferably 20 nm to 100 nm. The size of the voids (pores) can be adjusted to a desired size depending on the purpose, application, and the like.

Void (pore) size can be quantified by the BET test method. Specifically, 0.1 g of the sample (formed void layer) was put into the capillary of a specific surface area measuring device (manufactured by Micromeritic Co., Ltd.: ASAP2020), and then dried under reduced pressure for 24 hours at room temperature. Degas the gas within the structure. Then, by causing the sample to adsorb nitrogen gas, an adsorption isotherm is drawn to determine the pore size distribution. This allows the void size to be evaluated.

The haze of the low refractive index layer is, for example, less than 5%, preferably less than 3%. On the other hand, haze is, for example, 0.1% or more, preferably 0.2% or more. The range of haze is, for example, 0.1% or more and less than 5%, preferably 0.2% or more and less than 3%. Haze can be measured, for example, by the following method. Haze is an indicator of the transparency of the low refractive index layer.
The void layer (low refractive index layer) is cut into a size of 50 mm×50 mm and set in a haze meter (HM-150 manufactured by Murakami Color Research Laboratory Co., Ltd.) to measure the haze. The haze value is calculated using the following formula.
Haze (%) = [diffuse transmittance (%)/total light transmittance (%)] x 100 (%)

Examples of the low refractive index layer having voids therein include a porous layer and/or a low refractive index layer having at least a portion of an air layer. Porous layers typically include aerogels and/or particles (eg, hollow microparticles and/or porous particles). The low refractive index layer can preferably be a nanoporous layer (specifically, a porous layer in which 90% or more of the pores have a diameter in the range of 10 ⁻¹ nm to 10 ³ nm).

Any appropriate particles can be adopted as the particles. The particles are typically composed of silica-based compounds. Particle shapes include, for example, spherical, plate-like, needle-like, string-like, and grape cluster-like shapes. Examples of string-like particles include particles in which a plurality of particles having a spherical, plate-like, or needle-like shape are linked in a beaded shape, and short fiber-like particles (for example, the particles described in JP-A-2001-188104). short fibrous particles), and combinations thereof. String-like particles may be linear or branched. Grape cluster-like particles include, for example, grape cluster-like particles obtained by aggregating a plurality of spherical, plate-like, and needle-like particles. The shape of the particles can be confirmed, for example, by observing them with a transmission electron microscope.

The thickness of the low refractive index layer is preferably 0.2 μm to 5 μm, more preferably 0.3 μm to 3 μm. If the thickness of the low refractive index layer is within such a range, the breakage prevention effect of the present invention becomes remarkable. Furthermore, the desired thickness ratio can be easily achieved.

The low refractive index layer can be typically formed by coating or printing as described above. With such a configuration, the low refractive index layer can be continuously provided by roll-to-roll. Any appropriate method can be adopted for printing. Specifically, the printing method may be a plate-type printing method such as gravure printing, offset printing, or flexographic printing, or a plateless printing method such as inkjet printing, laser printing, or electrostatic printing. good.

An example of a specific configuration of the low refractive index layer will be described below. The low refractive index layer of this embodiment is composed of one type or a plurality of types of structural units that form a fine void structure, and the structural units are chemically bonded to each other through catalytic action. Examples of the shape of the structural unit include particulate, fibrous, rod-like, and tabular. A structural unit may have only one shape, or may have a combination of two or more shapes. In one embodiment, the low refractive index layer is a void layer made of a porous body composed of fine particles chemically bonded to each other. In the following, mainly, the case where the porous layer is composed of a porous body composed of chemically bonded fine particles will be described.

Such a void layer can be formed, for example, by chemically bonding microporous particles together in the void layer forming step. In addition, in the embodiment of the present invention, the shape of the "particle" (for example, the microporous particles) is not particularly limited, and may be, for example, spherical or other shape. Further, in the embodiment of the present invention, the microporous particles may be, for example, sol-gel beaded particles, nanoparticles (hollow nanosilica/nanoballoon particles), nanofibers, and the like. Microporous particles typically include inorganic material. Specific examples of inorganic substances include silicon (Si), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), and zirconium (Zr). These may be used alone or in combination of two or more. In one embodiment, the microporous particles are, for example, silicon compound microporous particles, and the porous body is, for example, a silicone porous body. The microporous particles of the silicon compound include, for example, pulverized gel-like silica compounds. Another form of the low refractive index layer having at least a portion of the porous layer and/or the air layer is, for example, made of fibrous substances such as nanofibers, and the fibrous substances are entangled to form voids. There are stratified void layers. The method for producing such a void layer is not particularly limited, and is, for example, the same as in the case of the void layer of the porous body in which the microporous particles are chemically bonded to each other. Still another form includes a void layer using hollow nanoparticles or nanoclay, and a void layer formed using hollow nanoballoons or magnesium fluoride. The void layer may be a void layer composed of a single constituent substance, or may be a void layer composed of a plurality of constituent substances. The void layer may be composed of a single form described above, or may be composed of a plurality of forms described above.

In the present embodiment, the porous structure of the porous body may be, for example, an open cell structure with continuous pore structures. The open cell structure means that the pore structure is three-dimensionally connected, for example, in the silicone porous material described above, and can be said to be a state in which the internal voids of the pore structure are continuous. Porosity can be increased by the porous body having an open-cell structure. However, when closed-cell particles (particles having individual pore structures) such as hollow silica are used, an open-cell structure cannot be formed. On the other hand, for example, when using silica sol particles (pulverized gel-like silicon compound that forms a sol), the particles have a three-dimensional dendritic structure, so the coating film (including pulverized gel-like silicon compound) By sedimentation and deposition of the dendritic particles in the sol coating film), it is possible to easily form an open cell structure. The low refractive index layer more preferably has a monolithic structure in which the open cell structure contains multiple pore distributions. A monolithic structure means, for example, a hierarchical structure including a structure in which nano-sized fine voids exist and an open-cell structure in which the nano-sized voids are aggregated. In the case of forming a monolithic structure, for example, it is possible to achieve both film strength and high porosity by imparting film strength with fine pores and imparting high porosity with coarse open-cell pores. Such a monolithic structure can be preferably formed by controlling the pore distribution of the void structure produced in the gel (gelled silicon compound) prior to pulverization into silica sol particles. Further, for example, when pulverizing the gelled silicon compound, a monolithic structure can be formed by controlling the particle size distribution of the silica sol particles after pulverization to a desired size.

The low refractive index layer contains, for example, pulverized gel compounds as described above, and the pulverized materials are chemically bonded to each other. The form of chemical bonding (chemical bonding) between pulverized particles in the low refractive index layer is not particularly limited, and examples thereof include cross-linking, covalent bonding, and hydrogen bonding.

The gel form of the gel compound is not particularly limited. "Gel" generally refers to a solidified state having a structure in which solutes lose their independent motility due to interactions and are aggregated. A gel compound may be, for example, a wet gel or a xerogel. In general, a wet gel contains a dispersion medium and the solute has a uniform structure in the dispersion medium, and a xerogel is a solution in which the solute has a network structure with voids after the solvent is removed. .

Gel compounds include, for example, gels obtained by gelling monomer compounds. Specifically, the gelled silicon compound includes, for example, a gelled product in which monomeric silicon compounds are bonded to each other, and specific examples include a gelled product in which monomeric silicon compounds are bonded to each other by covalent bonds, hydrogen bonds, or intermolecular forces. mentioned. Covalent bonds include, for example, dehydration-condensation bonds.

The volume average particle size of the pulverized material in the low refractive index layer is, for example, 0.10 μm or more, preferably 0.20 μm or more, and more preferably 0.40 μm or more. On the other hand, the volume average particle diameter is, for example, 2.00 μm or less, preferably 1.50 μm or less, more preferably 1.00 μm or less. The range of volume average particle diameter is, for example, 0.10 μm to 2.00 μm, preferably 0.20 μm to 1.50 μm, more preferably 0.40 μm to 1.00 μm. The particle size distribution can be measured by, for example, a particle size distribution evaluation device such as dynamic light scattering method and laser diffraction method, and an electron microscope such as scanning electron microscope (SEM) and transmission electron microscope (TEM). Incidentally, the volume average particle size is an index of the variation in the particle size of the pulverized material.

The type of gel compound is not particularly limited. Gel-like compounds include, for example, gel-like silicon compounds. Hereinafter, an example in which the gel compound is a gel silicon compound will be described, but the present invention is not limited to this.

The cross-linking bond is, for example, a siloxane bond. The siloxane bond includes, for example, a T2 bond, a T3 bond, and a T4 bond as shown below. When the void layer (low refractive index layer) has a siloxane bond, it may have any one type of bond, any two types of bond, or all three types of bond. good too. Among the siloxane bonds, the greater the ratio of T2 and T3, the more flexible the gel can be expected to have its inherent properties. On the other hand, the higher the T4 ratio, the easier it is for the film strength to develop. Therefore, it is preferable to change the ratio of T2, T3 and T4 depending on the purpose, application, desired properties, and the like.

In addition, in the low refractive index layer (void layer), for example, it is preferable that the silicon atoms contained are siloxane-bonded. As a specific example, the ratio of unbonded silicon atoms (that is, residual silanol) among all silicon atoms contained in the void layer is, for example, less than 50%, preferably 30% or less, more preferably 15%. It is below.

When the gel-like compound is a gel-like silicon compound, the monomer silicon compound is not particularly limited. Examples of the monomeric silicon compound include compounds represented by the following formula (1). When the gelled silicon compound is a gelled product in which the silicon compounds of the monomers are mutually hydrogen-bonded or intermolecularly bonded to each other as described above, the monomers of the formula (1) are, for example, hydrogen-bonded via their respective hydroxyl groups. can.

In formula (1), X is, for example, 2, 3 or 4, preferably 3 or 4. R ¹ is, for example, a straight-chain or branched alkyl group. The number of carbon atoms in R ¹ is, for example, 1-6, preferably 1-4, more preferably 1-2. Examples of straight-chain alkyl groups include methyl group, ethyl group, propyl group, butyl group, pentyl group and hexyl group, and examples of branched alkyl groups include isopropyl group and isobutyl group.

Specific examples of the silicon compound represented by formula (1) include compounds represented by the following formula (1′) in which X is 3. In formula (1′) below, R ¹ is the same as in formula (1), and is, for example, a methyl group. When R ¹ is a methyl group, the silicon compound is tris(hydroxy)methylsilane. When X is 3, the silicon compound is, for example, a trifunctional silane with three functional groups.

Another specific example of the silicon compound represented by formula (1) is a compound in which X is 4. In this case, the silicon compound is, for example, a tetrafunctional silane with four functional groups.

The monomeric silicon compound may be, for example, a hydrolyzate of a silicon compound precursor. Any silicon compound precursor can be used as long as it can be hydrolyzed to form a silicon compound, and specific examples thereof include compounds represented by the following formula (2).

In the formula (2), X is, for example, 2, 3 or 4,
R ¹ and R ² are each independently a linear or branched alkyl group;
R ¹ and R ² may be the same or different,
R ¹ may be the same or different when X is 2;
R ² may be the same or different from each other.

X and R ¹ are, for example, the same as X and R ¹ in formula (1). For R ² , for example, the examples of R ¹ in formula (1) can be used.

Specific examples of the silicon compound precursor represented by formula (2) include compounds represented by the following formula (2′) in which X is 3. In formula (2′) below, R ¹ and R ² are the same as in formula (2). When R ¹ and R ² are methyl groups, the silicon compound precursor is trimethoxy(methyl)silane (hereinafter also referred to as “MTMS”).

The monomeric silicon compound is preferably trifunctional silane, for example, from the viewpoint of excellent low refractive index properties. Moreover, the monomeric silicon compound is preferably a tetrafunctional silane, for example, from the viewpoint of excellent strength (for example, scratch resistance). Only one kind of the monomeric silicon compound may be used, or two or more kinds thereof may be used in combination. For example, the monomer silicon compound may contain only trifunctional silane, may contain only tetrafunctional silane, may contain both trifunctional silane and tetrafunctional silane, or may further contain other silicon compounds. It's okay. When two or more kinds of silicon compounds are used as the silicon compound of the monomer, the ratio is not particularly limited and can be set appropriately.

An example of a method for forming such a low refractive index layer will be described below.

The method typically comprises a precursor forming step of forming a void structure, which is a precursor of a low refractive index layer (void layer) on a resin film, and a cross-linking reaction inside the precursor after the precursor forming step. and a cross-linking reaction step that causes the The method includes a containing liquid preparation step of preparing a containing liquid containing microporous particles (hereinafter sometimes referred to as "microporous particle containing liquid" or simply "containing liquid"), and a drying step of drying the containing liquid. The method further includes a step of chemically bonding microporous particles in the dry body to form a precursor in the precursor forming step. The contained liquid is not particularly limited, and is, for example, a suspension containing microporous particles. In the following, mainly, the case where the microporous particles are pulverized gel compound and the void layer is a porous body (preferably silicone porous body) containing pulverized gel compound will be described. However, the low refractive index layer can be formed in the same manner even when the microporous particles are other than the pulverized gel compound.

According to the above method, for example, a low refractive index layer (void layer) having a very low refractive index is formed. The reason is presumed, for example, as follows. However, the assumption does not limit the method of forming the low refractive index layer.

Since the pulverized product is obtained by pulverizing the gel-like silicon compound, the three-dimensional structure of the gel-like silicon compound before pulverization is dispersed in the three-dimensional basic structure. Furthermore, in the above method, a precursor having a porous structure based on a three-dimensional basic structure is formed by coating a crushed gel-like silicon compound on a resin film. That is, according to the above method, a new porous structure (three-dimensional basic structure) is formed by coating the pulverized material, which is different from the three-dimensional structure of the gel-like silicon compound. Therefore, in the finally obtained void layer, a low refractive index that functions to the same extent as, for example, an air layer can be realized. Furthermore, in the above method, the three-dimensional basic structure is fixed because the crushed materials are chemically bonded to each other. Therefore, the void layer finally obtained can maintain sufficient strength and flexibility in spite of having a structure having voids.

Furthermore, in the above method, the precursor forming step and the cross-linking reaction step are performed as separate steps. In addition, the cross-linking reaction step is preferably carried out in multiple stages. By performing the cross-linking reaction step in multiple steps, for example, compared to performing the cross-linking reaction step in one step, the strength of the precursor is further improved, and a low refractive index layer having both high porosity and strength can be obtained. Although this mechanism is unknown, it is presumed, for example, as follows. That is, as described above, if the membrane strength is improved by a catalyst or the like at the same time as the formation of the void layer, the progress of the catalytic reaction increases the membrane strength but decreases the porosity. This is because, for example, the number of cross-links (chemical bonds) between micro-porous particles increases due to the progress of a cross-linking reaction between micro-porous particles by a catalyst, and the bonds become stronger, but the entire void layer is condensed. This is probably because the porosity decreases. On the other hand, by performing the precursor formation step and the cross-linking reaction step as separate steps, and performing the cross-linking reaction step in multiple steps, for example, without significantly changing the form of the whole precursor (for example, the whole It is believed that the number of crosslinks (chemical bonds) can be increased without causing too much condensation. However, these are only examples of conjecturable mechanisms, and do not limit the method of forming the low refractive index layer.

In the precursor forming step, for example, particles having a certain shape are laminated to form the precursor of the void layer. The strength of the precursor at this point is very weak. Thereafter, for example, a photo- or thermally-activated catalytic reaction is used to generate a product that can chemically bond the microporous particles together (e.g., a strong base catalyst generated from a photobase generator, etc.) (one step of the cross-linking reaction process). eye). It is believed that further heat aging (the second stage of the cross-linking reaction process) is performed to efficiently advance the reaction in a short time, thereby further promoting chemical bonding (cross-linking reaction) between the microporous particles and improving the strength. For example, when the microporous particles are microporous particles of a silicon compound (for example, a pulverized gel-like silica compound) and residual silanol groups (Si—OH groups) are present in the precursor, the residual silanol groups are crosslinked. It is believed that chemical bonding occurs through a reaction. However, this description is also an example, and does not limit the method of forming the low refractive index layer.

The above method has a containing liquid preparation step of preparing a containing liquid containing microporous particles. When the microporous particles are a pulverized product of a gel compound, the pulverized product is obtained, for example, by pulverizing the gel compound. By pulverizing the gel-like compound, the three-dimensional structure of the gel-like compound is destroyed and dispersed into three-dimensional basic structures, as described above. An example of preparation of the pulverized material is as follows.

Gelation of the monomeric compound can be performed, for example, by hydrogen bonding or intermolecular force bonding of the monomeric compounds to each other. Examples of monomer compounds include silicon compounds represented by the above formula (1). Since the silicon compound of formula (1) has a hydroxyl group, hydrogen bonding or intermolecular force bonding is possible between the monomers of formula (1) via the respective hydroxyl groups, for example.

Alternatively, the silicon compound may be a hydrolyzate of the above silicon compound precursor, for example, it may be produced by hydrolyzing the silicon compound precursor represented by formula (2) above.

The method for hydrolyzing the monomer compound precursor is not particularly limited, and can be carried out, for example, by chemical reaction in the presence of a catalyst. Examples of catalysts include acids such as oxalic acid and acetic acid. The hydrolysis reaction is carried out, for example, by slowly dropping and mixing an aqueous solution of oxalic acid with a mixed solution (e.g., suspension) of a silicon compound and dimethyl sulfoxide at room temperature, and then stirring the solution for about 30 minutes. be able to. When hydrolyzing the silicon compound precursor, for example, by completely hydrolyzing the alkoxy groups of the silicon compound precursor, the subsequent gelation, aging, and heating and fixing after formation of the pore structure can be made more efficient. It can be carried out.

Gelation of a monomer compound can be performed, for example, by a dehydration condensation reaction between monomers. The dehydration condensation reaction is preferably carried out, for example, in the presence of a catalyst. Examples of catalysts include acid catalysts such as hydrochloric acid, oxalic acid, and sulfuric acid, and bases such as ammonia, potassium hydroxide, sodium hydroxide, and ammonium hydroxide. Dehydration condensation catalysts such as catalysts can be mentioned. A base catalyst is preferable as the dehydration condensation catalyst. In the dehydration condensation reaction, the amount of catalyst added to the monomer compound is not particularly limited. The catalyst may be added, for example, in an amount of preferably 0.1 mol to 10 mol, more preferably 0.05 mol to 7 mol, still more preferably 0.1 mol to 5 mol, per 1 mol of the monomer compound.

Gelation of the monomer compound is preferably carried out, for example, in a solvent. The ratio of the monomer compound to the solvent is not particularly limited. Solvents include, for example, dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), γ-butyllactone (GBL), acetonitrile (MeCN), ethylene Glycol ethyl ether (EGEE) and the like are included. The solvent may be used alone or in combination of two or more. Hereinafter, the solvent used for gelation is also referred to as "gelation solvent".

Gelation conditions are not particularly limited. The treatment temperature for the solvent containing the monomer compound is, for example, 20°C to 30°C, preferably 22°C to 28°C, more preferably 24°C to 26°C. The treatment time is, for example, 1 minute to 60 minutes, preferably 5 minutes to 40 minutes, more preferably 10 minutes to 30 minutes. When the dehydration condensation reaction is performed, the treatment conditions are not particularly limited, and these examples can be used. By performing gelation, for example, siloxane bonds grow, silica primary particles are formed, and the reaction proceeds, so that the primary particles are linked together in a beaded shape to form a gel with a three-dimensional structure.

A gel-like compound obtained by gelling is preferably subjected to aging treatment after the gelling reaction. The aging treatment can, for example, further grow the primary particles of the gel having a three-dimensional structure obtained by gelation and increase the size of the particles themselves. It is possible to change the contact state of the neck portion where the contact is made from point contact to surface contact (increase the contact area). A gel that has undergone an aging treatment has, for example, increased strength of the gel itself, and as a result, the strength of the three-dimensional basic structure after pulverization can be improved. As a result, for example, in the drying process after applying the pulverized material, it is possible to suppress the shrinkage of the pore size of the void structure in which the three-dimensional basic structure is deposited due to the volatilization of the solvent during the drying process.

Aging treatment can be performed, for example, by incubating the gel-like compound at a predetermined temperature for a predetermined time. The aging temperature is, for example, 30° C. or higher, preferably 35° C. or higher, more preferably 40° C. or higher. On the other hand, the aging temperature is, for example, 80° C. or lower, preferably 75° C. or lower, more preferably 70° C. or lower. The range of aging temperature is, for example, 30°C to 80°C, preferably 35°C to 75°C, more preferably 40°C to 70°C. The aging time is, for example, 5 hours or longer, preferably 10 hours or longer, and more preferably 15 hours or longer. On the other hand, the aging time is, for example, 50 hours or less, preferably 40 hours or less, more preferably 30 hours or less. The range of aging time is, for example, 5 hours to 50 hours, preferably 10 hours to 40 hours, more preferably 15 hours to 30 hours. The ripening conditions can be optimized, for example, to obtain an increase in the silica primary particle size and an increase in the contact area of the neck portion. Furthermore, it is preferable to consider the boiling point of the solvent used. There is a possibility that problems such as clogging of pores may occur. On the other hand, for example, if the aging temperature is too low, not only is the effect of aging not sufficiently obtained, but the temperature variation increases over time in the mass production process, which may result in the formation of a low refractive index layer with inferior properties. have a nature.

For the aging treatment, for example, the same solvent as for the gelation treatment can be used. Specifically, it is preferable to subject the reactant (that is, the solvent containing the gel-like compound) after the gel treatment to the aging treatment as it is. The number of moles of residual silanol groups contained in the gel (gel-like compound, for example, gel-like silicon compound) that has undergone aging treatment after gelation is, for example, 50% or less, preferably 40% or less, and more preferably. is 30% or less. On the other hand, the number of moles of residual silanol groups is, for example, 1% or more, preferably 3% or more, and more preferably 5% or more. The range of the number of moles of residual silanol groups is, for example, 1% to 50%, preferably 3% to 40%, more preferably 5% to 30%. For the purpose of increasing gel hardness, for example, the lower the number of moles of residual silanol groups, the better. If the number of moles of silanol groups is too high, for example, the void structure may not be maintained until the precursor of the porous silicone material is crosslinked. On the other hand, if the number of moles of silanol groups is too low, for example, in the step of preparing a microporous particle-containing liquid (e.g., suspension) and/or in subsequent steps, the pulverized gel-like compound cannot be crosslinked. It may not be possible to provide sufficient film strength. The number of moles of residual silanol groups is, for example, the ratio of residual silanol groups when the number of moles of alkoxy groups in the raw material (eg, monomer compound precursor) is 100. Although the above is an example of a silanol group, for example, when the silicon compound of the monomer is modified with various reactive functional groups, the same matters and conditions can be applied to each functional group.

After the monomer compound is gelled in the gelling solvent, the obtained gelled compound is pulverized. For pulverization, for example, the gel compound in the gelling solvent may be directly pulverized, or the gelling solvent may be replaced with another solvent and then the gel compound in the other solvent may be pulverized. A pulverization treatment may be applied to the compound. Further, for example, if the catalyst used in the gelation reaction and the solvent used remain after the aging process, causing gelation of the liquid over time (pot life) and a decrease in drying efficiency during the drying process, other Substitution with a solvent is preferred. The above-mentioned other solvent is hereinafter also referred to as "pulverization solvent".

The solvent for pulverization is not particularly limited, and for example, an organic solvent can be used. Examples of organic solvents include solvents having a boiling point of 130° C. or lower, preferably 100° C. or lower, and more preferably 85° C. or lower. Specific examples include isopropyl alcohol (IPA), ethanol, methanol, butanol, propylene glycol monomethyl ether (PGME), methyl cellosolve, acetone, dimethylformamide (DMF), isobutyl alcohol and the like. The grinding solvent may be used alone or in combination of two or more.

The combination of the gelling solvent and the grinding solvent is not particularly limited, and examples thereof include combinations of DMSO and IPA, DMSO and ethanol, DMSO and methanol, DMSO and butanol, and DMSO and isobutyl alcohol. By substituting the gelling solvent with the crushing solvent in this manner, for example, a more uniform coating film can be formed in the coating film formation described later.

The method of pulverizing the gel-like compound is not particularly limited, and for example, it can be carried out by using an ultrasonic homogenizer, a high-speed rotary homogenizer, or other pulverizing devices using the cavitation phenomenon. Devices that perform media pulverization such as ball mills, for example, physically destroy the void structure of the gel during pulverization, whereas cavitation type pulverization devices such as homogenizers, for example, are medialess, so the gel has a three-dimensional structure. A high-speed shearing force is applied to peel off the relatively weakly bonded silica particle bonding surface that is already included. As a result, the resulting three-dimensional gel structure can retain, for example, a pore structure having a particle size distribution within a certain range, and the pore structure can be re-formed by deposition during coating and drying. Pulverization conditions are not particularly limited, and for example, it is preferable that the gel can be pulverized without volatilizing the solvent by instantaneously applying a high-speed flow. For example, it is preferable to pulverize so as to obtain a pulverized product having the above-described particle size variations (for example, volume average particle size or particle size distribution). If the amount of work such as pulverization time and strength is insufficient, for example, coarse particles will remain and not only fine pores cannot be formed, but also appearance defects will increase, and high quality may not be obtained. On the other hand, if the amount of work is excessive, for example, the particles become finer than the desired particle size distribution, the pore size deposited after coating and drying becomes fine, and the desired porosity may not be obtained.

As described above, a liquid (for example, a suspension) containing microporous particles (pulverized gel compound) can be prepared. Furthermore, a containing liquid containing microporous particles and a catalyst can be produced by adding a catalyst that chemically bonds the microporous particles together after producing the liquid containing the microporous particles or during the production process. . The catalyst may be, for example, a catalyst that promotes cross-linking between microporous particles. As a chemical reaction for chemically bonding the microporous particles, it is preferable to use a dehydration condensation reaction of residual silanol groups contained in the silica sol molecules. By promoting the reaction between the hydroxyl groups of the silanol groups with a catalyst, it is possible to form a continuous film that hardens the pore structure in a short time. Catalysts include, for example, photoactivated catalysts and thermally activated catalysts. A photoactive catalyst can chemically bond (for example, crosslink) microporous particles without heating in a precursor forming step, for example. According to this, for example, in the precursor formation step, shrinkage of the entire precursor is less likely to occur, so a higher porosity can be maintained. In addition to or instead of the catalyst, a substance that generates a catalyst (catalyst generator) may be used. For example, in addition to or instead of the photoactive catalyst, a substance that generates a catalyst by light (photocatalyst generator) may be used, or in addition to or instead of the thermally active catalyst, a catalyst may be generated by heat. A substance (thermal catalyst generator) may be used. Examples of photocatalyst generators include photobase generators (substances that generate basic catalysts by light irradiation), photoacid generators (substances that generate acidic catalysts by light irradiation), and the like. preferable. Examples of photobase generators include 9-anthrylmethyl N,N-diethylcarbamate (9-anthrylmethyl N,N-diethylcarbamate, trade name WPBG-018), (E)-1-[3-(2-hydroxy Phenyl)-2-propenoyl]piperidine ((E)-1-[3-(2-hydroxyphenyl)-2-propenoyl]piperidine, trade name WPBG-027), 1-(anthraquinon-2-yl)ethyl imidazole carboxylate (1-(anthraquinon-2-yl)ethyl imidazolecarboxylate, trade name WPBG-140), 2-nitrophenylmethyl 4-methacryloyloxypiperidine-1-carboxylate (trade name WPBG-165), 1,2-diisopropyl-3 -[bis(dimethylamino)methylene]guanidinium 2-(3-benzoylphenyl)propionate (trade name WPBG-266), 1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidinium n-butyltri Phenylborate (trade name WPBG-300), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene 2-(9-oxoxanthen-2-yl)propionate (Tokyo Kasei Kogyo Co., Ltd.), a compound containing 4-piperidinemethanol (trade name HDPD-PB100: manufactured by Heraeus), and the like. All product names including "WPBG" are product names of Wako Pure Chemical Industries, Ltd. Examples of photoacid generators include aromatic sulfonium salts (trade name SP-170: ADEKA), triarylsulfonium salts (trade name CPI101A: Sun-Apro Co.), aromatic iodonium salts (trade name Irgacure250: Ciba Japan). ) and the like. Further, the catalyst that chemically bonds the microporous particles together is not limited to the photoactive catalyst and the photocatalyst generator, and may be, for example, a thermally activated catalyst or a thermal catalyst generator such as urea. Examples of the catalyst for chemically bonding microporous particles include base catalysts such as potassium hydroxide, sodium hydroxide and ammonium hydroxide, and acid catalysts such as hydrochloric acid, acetic acid and oxalic acid. Among these, base catalysts are preferred. A catalyst or catalyst generator that chemically bonds microporous particles together is used, for example, by adding it to a sol particle liquid (e.g., suspension) containing pulverized particles (microporous particles) immediately before coating, or A mixture of a catalyst or a catalyst generator and a solvent can be used. The mixed liquid may be, for example, a coating liquid directly added and dissolved in the sol particle liquid, a solution in which a catalyst or a catalyst generator is dissolved in a solvent, or a dispersion liquid in which a catalyst or a catalyst generator is dispersed in a solvent. Solvents are not particularly limited, and examples thereof include water, buffer solutions, and the like.

Further, for example, the gel-containing liquid may further contain a cross-linking auxiliary agent for indirectly binding the crushed pieces of the gel. The cross-linking aid enters between the particles (the pulverized material), and the particles and the cross-linking aid interact or bond with each other, so that even particles that are somewhat distant from each other can be bonded together, It is possible to increase strength efficiently. A multi-crosslinked silane monomer is preferable as the cross-linking aid. Specifically, the polycrosslinked silane monomer has, for example, 2 to 3 alkoxysilyl groups, and the chain length between the alkoxysilyl groups may be 1 to 10 carbon atoms, and an element other than carbon may also include Examples of the crosslinking aid include bis(trimethoxysilyl)ethane, bis(triethoxysilyl)ethane, bis(trimethoxysilyl)methane, bis(triethoxysilyl)methane, bis(triethoxysilyl)propane, bis (trimethoxysilyl)propane, bis(triethoxysilyl)butane, bis(trimethoxysilyl)butane, bis(triethoxysilyl)pentane, bis(trimethoxysilyl)pentane, bis(triethoxysilyl)hexane, bis(tri methoxysilyl)hexane, bis(trimethoxysilyl)-N-butyl-N-propyl-ethane-1,2-diamine, tris-(3-trimethoxysilylpropyl) isocyanurate, tris-(3-triethoxysilylpropyl ) isocyanurate and the like. The amount of the cross-linking aid added is not particularly limited. % by weight.

Next, a liquid containing microporous particles (such as a suspension) is applied onto the sealing portion (coating step). For coating, for example, various coating methods described later can be used, and the coating is not limited to these. A coating film containing microporous particles and a catalyst can be formed by directly applying a liquid containing microporous particles (for example, pulverized gel-like silica compound) onto the sealing portion. The coating film can also be called a coating layer, for example. A new three-dimensional structure is constructed by forming a coating film, for example, by sedimenting and depositing pulverized materials whose three-dimensional structure is destroyed. It should be noted that, for example, the liquid containing microporous particles may not contain a catalyst that chemically bonds microporous particles together. For example, as will be described later, the precursor formation step may be performed after or while spraying a catalyst that chemically bonds microporous particles to the coating film. However, the liquid containing the microporous particles contains a catalyst that chemically bonds the microporous particles, and the action of the catalyst contained in the coating film causes the microporous particles to chemically bond to form a porous body. may form a precursor of

The solvent (hereinafter also referred to as "coating solvent") is not particularly limited, and for example, an organic solvent can be used. Examples of organic solvents include solvents having a boiling point of 150° C. or less. Specific examples include IPA, ethanol, methanol, n-butanol, 2-butanol, isobutyl alcohol, pentanol and the like, and the same solvents as those for pulverization can be used. When the method for forming the low refractive index layer includes the step of pulverizing the gel compound, in the step of forming the coating film, for example, a pulverization solvent containing the pulverized product of the gel compound may be used as it is. .

In the coating step, for example, a sol-like pulverized material dispersed in a solvent (hereinafter also referred to as “sol particle liquid”) is preferably coated on the sealing portion. For example, the sol particle liquid is applied onto the sealing portion, dried, and then subjected to the chemical cross-linking, whereby a void layer having a film strength of a certain level or more can be continuously formed. In addition, the "sol" in the embodiment of the present invention means that the three-dimensional structure of the gel is pulverized, and silica sol particles with a nano-three-dimensional structure that retain a part of the void structure are dispersed in the solvent and have fluidity. It means the state shown.

The concentration of the pulverized product in the coating solvent is not particularly limited, and is, for example, 0.3% (v/v) to 50% (v/v), preferably 0.5% (v/v) to 30% (v/v). % (v/v), more preferably 1.0% (v/v) to 10% (v/v). If the concentration of the pulverized material is too high, for example, the fluidity of the sol particle liquid is significantly lowered, and there is a possibility that aggregates and coating streaks may occur during coating. If the concentration of the pulverized material is too low, for example, not only will it take a considerable amount of time to dry the solvent in the sol particle liquid, but the amount of residual solvent will increase immediately after drying, which may result in a decrease in porosity. .

Physical properties of the sol are not particularly limited. The shear viscosity of the sol at a shear rate of 10001/s is, for example, 100 cPa·s or less, preferably 10 cPa·s or less, more preferably 1 cPa·s or less. If the shear viscosity is too high, for example, coating streaks may occur, and problems such as a decrease in the transfer rate of gravure coating may be observed. Conversely, if the shear viscosity is too low, for example, the wet coating thickness during coating cannot be increased, and the desired thickness may not be obtained after drying.

The amount of the pulverized product to be applied is not particularly limited, and can be set as appropriate according to, for example, the desired thickness of the silicone porous body (resulting in the low refractive index layer). As a specific example, when forming a silicone porous body with a thickness of 0.1 μm to 1000 μm, the coating amount of the pulverized material is, for example, 0.01 μg to 60000 μg, preferably 0.1 μg to 60000 μg, per 1 m ² of the area of the coated surface. 5000 μg, more preferably 1 μg to 50 μg. The preferred coating amount of the sol particle liquid is related to, for example, the concentration of the liquid and the coating method, so it is difficult to define it unambiguously. preferable. If the coating amount is too large, for example, the possibility of drying in a drying oven before the solvent volatilizes increases. As a result, the nano-pulverized sol particles settle and accumulate in the solvent, and the solvent dries before forming a void structure, which may hinder the formation of voids and greatly reduce the porosity. On the other hand, if the coating amount is too thin, the risk of coating repellency may increase.

Furthermore, the method for forming the low refractive index layer has, for example, a precursor forming step of forming a void structure, which is a precursor of the void layer (low refractive index layer), as described above. The precursor forming step is not particularly limited, but for example, the precursor (void structure) may be formed by a drying step of drying a coating film prepared by applying a microporous particle-containing liquid. The drying process in the drying process not only removes the solvent in the coating film (solvent contained in the sol particle liquid), but also causes the sol particles to settle and deposit during the drying process to form a void structure. can do. The temperature of the drying treatment is, for example, 50°C to 250°C, preferably 60°C to 150°C, more preferably 70°C to 130°C. The drying time is, for example, 0.1 to 30 minutes, preferably 0.2 to 10 minutes, more preferably 0.3 to 3 minutes.

The drying treatment may be, for example, natural drying, drying by heating, or drying under reduced pressure. Among them, it is preferable to use heat drying when continuous industrial production is assumed. The method of drying by heating is not particularly limited, and for example, general heating means can be used. Examples of heating means include a hot air blower, a heating roll, and a far-infrared heater. As for the solvent to be used, a solvent having a low surface tension is preferable for the purpose of suppressing the generation of shrinkage stress due to volatilization of the solvent during drying and the resulting cracking phenomenon of the void layer (silicone porous body). Examples of solvents include lower alcohols such as isopropyl alcohol (IPA), hexane, and perfluorohexane. Also, a small amount of perfluoro-based surfactant or silicone-based surfactant may be added to the IPA or the like to lower the surface tension.

Furthermore, as described above, the method for forming the low refractive index layer includes a cross-linking reaction step of causing a cross-linking reaction inside the precursor after the precursor forming step. is generated, and the cross-linking reaction process is multi-step. In the first stage of the cross-linking reaction process, for example, microporous particles are chemically bonded together by the action of a catalyst (basic substance). Thereby, for example, the three-dimensional structure of the pulverized material in the coating film (precursor) is fixed. In the case of fixing by conventional sintering, for example, high-temperature treatment at 200° C. or higher induces dehydration condensation of silanol groups and formation of siloxane bonds. In this forming method, by reacting various additives that catalyze the dehydration condensation reaction, for example, at a relatively low drying temperature of around 100 ° C. and a short treatment time of less than several minutes, a continuous void structure can be formed and immobilized.

A method of chemically bonding is not particularly limited, and can be appropriately determined according to, for example, the type of gelled silicon compound. As a specific example, chemical bonding can be achieved, for example, by chemical cross-linking between pulverized products. It is also conceivable to chemically cross-link the material and the pulverized product. In addition, when a biocatalyst such as an enzyme is supported, a site other than the catalytic active site may be chemically cross-linked with the pulverized material. Therefore, the method of forming the low refractive index layer is not limited to a porous layer (silicone porous body) formed by sol particles, but can be applied to organic-inorganic hybrid porous layers, host-guest porous layers, and the like.

The chemical reaction in the presence of the catalyst is not particularly limited at which stage in the method of forming the low refractive index layer, and is performed, for example, at least one stage in the multi-step cross-linking reaction process. For example, in the method for forming the low refractive index layer, the drying step may serve as the precursor forming step as described above. Further, for example, after the drying process, a multi-stage cross-linking reaction process may be performed, and the microporous particles may be chemically bonded to each other by the action of a catalyst in at least one of the stages. For example, when the catalyst is a photoactive catalyst as described above, the microporous particles may be chemically bonded to each other by light irradiation in the cross-linking reaction step to form a precursor of the porous body. Further, when the catalyst is a thermally activated catalyst, the microporous particles may be chemically bonded to each other by heating in the cross-linking reaction step to form a precursor of the porous body.

The above-mentioned chemical reaction can be performed, for example, by irradiating or heating a coating film containing a catalyst previously added to a sol particle liquid (e.g., suspension), or by spraying a catalyst on a coating film and then irradiating or heating the catalyst. Alternatively, it can be carried out by light irradiation or heating while spraying the catalyst. The integrated amount of light in the light irradiation is not particularly limited, and is, for example, 200 mJ/cm ² to 800 mJ/cm ² , preferably 250 mJ/cm ² to 600 mJ/cm ² , more preferably 300 mJ/cm in terms of a wavelength of 360 nm. ² to 400 mJ/cm ² . From the viewpoint of preventing insufficient effects due to insufficient irradiation due to insufficient decomposition due to light absorption of the catalyst, an integrated light amount of 200 mJ/cm ² or more is preferable. Conditions for the heat treatment are not particularly limited. The heating temperature is, for example, 50°C to 250°C, preferably 60°C to 150°C, more preferably 70°C to 130°C. The heating time is, for example, 0.1 to 30 minutes, preferably 0.2 to 10 minutes, more preferably 0.3 to 3 minutes. Alternatively, the step of drying the coated sol particle liquid (eg, suspension) may also serve as the step of performing a chemical reaction in the presence of a catalyst. That is, in the step of drying the coated sol particle liquid (for example, suspension), pulverized materials (microporous particles) may be chemically bonded to each other by a chemical reaction in the presence of a catalyst. In this case, by further heating the coating film after the drying step, the pulverized materials (microporous particles) may be bonded together more firmly. Furthermore, it is presumed that the chemical reaction in the presence of a catalyst may also occur in the step of preparing a microporous particle-containing liquid (eg suspension) and the step of applying the microporous particle-containing liquid. However, this speculation does not limit the formation method of the low refractive index layer. As for the solvent to be used, for example, a solvent having a low surface tension is preferable for the purpose of suppressing the generation of shrinkage stress due to volatilization of the solvent during drying and the resulting cracking phenomenon of the void layer. Examples include lower alcohols such as isopropyl alcohol (IPA), hexane, and perfluorohexane.

In the method for forming the low refractive index layer, since the cross-linking reaction step is performed in multiple steps, the strength of the void layer (low refractive index layer) can be further improved compared to the case where the cross-linking reaction step is performed in one step, for example. can. Hereinafter, the steps after the second step of the cross-linking reaction step may be referred to as "aging step". In the aging step, for example, the precursor may be heated to further promote the cross-linking reaction inside the precursor. Although the phenomenon and mechanism that occur in the cross-linking reaction step are unknown, they are, for example, as described above. For example, in the aging step, the heating temperature is set to a low temperature to cause a cross-linking reaction while suppressing shrinkage of the precursor, thereby improving strength and achieving both high porosity and strength. The temperature in the aging step is, for example, 40°C to 70°C, preferably 45°C to 65°C, more preferably 50°C to 60°C. The time for performing the aging process is, for example, 10 hr to 30 hr, preferably 13 hr to 25 hr, more preferably 15 hr to 20 hr.

Since the low refractive index layer formed as described above is excellent in strength, it can be made into, for example, a roll-shaped porous body, which has advantages such as good manufacturing efficiency and easy handling.

The low refractive index layer (void layer) thus formed may be laminated with another film (layer) to form a laminated structure including a porous structure. In this case, each constituent element in the laminated structure may be laminated via a pressure-sensitive adhesive or an adhesive, for example.

Details of the specific configuration and formation method of the low refractive index layer are described, for example, in International Publication No. 2019/151073. The description of the publication is incorporated herein by reference.

C. Micro LED Array Substrate As the micro LED array substrate, any suitable micro LED array substrate can be used. Typically, as shown in FIG. 1, the micro LED array substrate 10 includes a drive substrate 12 and a plurality of micro LEDs 11 arranged in a matrix on the drive substrate 12 .

A micro LED means an LED whose chip size is, for example, 1 μm square to 100 μm square.

In one embodiment, a single type of micro LED can be used as the plurality of micro LEDs. In one embodiment, the micro LEDs are blue LEDs or UV LEDs.

The drive substrate may be configured to individually switch drive the micro LEDs. Since the driving substrate is well known to those skilled in the art, the description is omitted here.

D. Encapsulation The encapsulation may be made of any suitable transparent material. Examples of the material forming the sealing portion include epoxy-based resin, silicone-based resin, acrylic-based resin, and the like. Moreover, the sealing portion may be formed of molten glass. Examples of the glass constituting the sealing portion include acrylic glass, crown glass, flint glass, borosilicate glass, and the like.

The sealing portion may be composed of an adhesive or a pressure-sensitive adhesive. In one embodiment, the sealing portion is composed of an adhesive.

Any appropriate adhesive can be used as the adhesive. Examples include water-based adhesives such as isocyanate-based, polyvinyl alcohol-based, gelatin-based, vinyl-based latex-based, water-based polyurethane, and water-based polyester, UV-curable adhesives, and curable adhesives such as electron beam-curable adhesives. .

Any appropriate adhesive can be used as the adhesive. Examples thereof include rubber-based, acrylic, silicone-based, urethane-based, vinyl alkyl ether-based, polyvinyl alcohol-based, polyvinylpyrrolidone-based, polyacrylamide-based, and cellulose-based adhesives. Among them, acrylic pressure-sensitive adhesives are preferably used because they are excellent in optical transparency, adhesion properties, weather resistance, heat resistance, and the like.

The sealing portion may have a light transmittance (23° C.) at a wavelength of 590 nm, for example, of 80% or more, preferably 85% or more, and more preferably 90% or more. Also, the average light transmittance of the sealing portion at a wavelength of 450 nm to 500 nm is preferably 70% or more, more preferably 75% or more, and still more preferably 80% or more. Also, the average light transmittance of the sealing portion at a wavelength of 500 nm to 780 nm is preferably 80% or more, more preferably 85% or more, and still more preferably 90% or more.

The refractive index of the sealing portion is preferably 1.40 or more, more preferably 1.40 to 2.00, still more preferably 1.45 to 1.80.

The thickness of the sealing portion is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less. If the thickness of the sealing portion is reduced, the effect of suppressing color mixture becomes remarkable. The lower limit of the thickness of the sealing portion is, for example, 10 μm. The thickness of the sealing portion may be the distance from the surface of the micro LED on the low refractive index layer side to the surface of the sealing portion on the micro LED side.

E. Wavelength Conversion Layer The wavelength conversion layer is a layer that absorbs excitation light from the micro LED and emits light of a predetermined color. When a blue LED is used as the micro LED, a red sub-pixel is formed by a wavelength conversion layer that absorbs excitation light from the micro LED and emits red light, and a wavelength conversion layer that absorbs the excitation light and emits green light forms a red sub-pixel. A green subpixel can be formed. Further, when an ultraviolet LED is used, a red sub-pixel is formed by a wavelength conversion layer that emits red light when excited by ultraviolet light, and a green sub-pixel is formed by a wavelength conversion layer that emits green light when excited by ultraviolet light. A blue sub-pixel is formed by a wavelength converting layer that emits blue light when excited by .

In one embodiment, the wavelength converting layer comprises phosphor particles. A wavelength converting layer typically includes a matrix and phosphor particles dispersed in the matrix. Any appropriate material can be used as the material that constitutes the matrix (hereinafter also referred to as matrix material). Such materials include resins, organic oxides, and inorganic oxides. The matrix material is preferably resin. The resin may be a thermoplastic resin, a thermosetting resin, or an active energy ray-curable resin (for example, an electron beam-curable resin, an ultraviolet-curable resin, a visible light-curable resin). may A thermosetting resin or an ultraviolet curable resin is preferred, and a thermosetting resin is more preferred. The resins may be used alone or in combination (eg, blended, copolymerized).

In one embodiment, quantum dots can be used as phosphor particles. Quantum dots can control the wavelength conversion properties of the wavelength converting layer. Specifically, by appropriately combining quantum dots having different emission center wavelengths, it is possible to form a wavelength conversion layer that realizes light having a desired emission center wavelength. The emission central wavelength of the quantum dots can be adjusted by the material and/or composition, particle size, shape, etc. of the quantum dots. As quantum dots, for example, quantum dots having an emission central wavelength in a wavelength band of 600 nm to 680 nm (hereinafter, quantum dots A), quantum dots having an emission central wavelength in a wavelength band of 500 nm to 600 nm (hereinafter, Quantum dots B) and quantum dots having an emission center wavelength in the wavelength band of 400 nm to 500 nm (hereinafter referred to as quantum dots C) are known. Quantum dot A is excited by excitation light (light from the micro LED) and emits red light, quantum dot B emits green light, and quantum dot C emits blue light. By appropriately combining these, light having a central emission wavelength in a desired wavelength band can be realized by allowing light of a predetermined wavelength to enter and pass through the wavelength conversion layer.

Quantum dots may be composed of any suitable material. Quantum dots may preferably be composed of inorganic materials, more preferably inorganic conductor or semiconductor materials. Semiconductor materials include, for example, Groups II-VI, III-V, IV-VI, and IV semiconductors. Specific examples include Si, Ge, Sn, Se, Te, B, C (including diamond), P, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdSeZn, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr, CuI, _Si3N4 , _Ge3N4 , _{Al2O3 ,} (Al, Ga, _In ) ₂ (S, Se, Te) _{3 , Al2} CO can be mentioned. These may be used alone or in combination of two or more. The quantum dots may contain p-type dopants or n-type dopants.

Any appropriate size can be adopted for the size of the quantum dots depending on the desired emission wavelength. The size of the quantum dots is preferably between 1 nm and 10 nm, more preferably between 2 nm and 8 nm. If the size of the quantum dots is within such a range, each of green and red emits sharp luminescence, and high color rendering properties can be achieved. For example, green light may be emitted at quantum dot sizes of the order of 7 nm, and red light may be emitted at the order of 3 nm. The size of a quantum dot is the average particle diameter if the quantum dot is spherical, for example, and the dimension along the minimum axis of the shape if the quantum dot is of another shape. Any appropriate shape can be adopted as the shape of the quantum dots depending on the purpose. Specific examples include a spherical shape, a scaly shape, a plate shape, an ellipsoidal shape, and an irregular shape.

Quantum dots can be blended in a proportion of preferably 1 to 50 parts by weight, more preferably 2 to 30 parts by weight, with respect to 100 parts by weight of the matrix material. If the compounding amount of the quantum dots is within such a range, it is possible to provide a display excellent in hue balance of all RGB.

Details of quantum dots, for example, JP 2012-169271, JP 2015-102857, JP 2015-65158, JP 2013-544018, JP 2013-544018, JP 2010-533976, and the descriptions in these publications are incorporated herein by reference. A commercial item may be used for the quantum dot.

In another embodiment, the phosphor particles are particles that exhibit luminescence due to their composition. Such phosphor particles include, for example, sulfide, aluminate, oxide, silicate, nitride, YAG, terbium aluminum garnet (TAG) based materials.

Further, the following red phosphors and green phosphors may be used as the phosphor particles. Red phosphors include, for example, Mn ⁴⁺ -activated composite fluoride phosphors. A composite fluoride phosphor contains at least one coordination center (e.g., M described later), is surrounded by fluoride ions acting as ligands, and optionally includes counter ions (e.g., A described later). ) refers to a coordination compound whose charge is compensated by ). Specific examples thereof include A ₂ [MF ₅ ]: Mn ⁴⁺ , A ₃ [MF ₆ ]: Mn ⁴⁺ , Zn ₂ [MF ₇ ]: Mn ⁴⁺ , A[In ₂ F ₇ ]: Mn ⁴⁺ , A ₂ [ _M'F6 ]:Mn4 ⁺ , E[ _M'F6 ]: _Mn4 ⁺ , A3[ _ZrF7 ]: _Mn4 ⁺ , _{Ba0.65Zr0.35F2.70} : _Mn4 ⁺ . where A is Li, Na, K, Rb, Cs, _NH4 or a combination thereof. M is Al, Ga, In or a combination thereof. M' is Ge, Si, Sn, Ti, Zr, or a combination thereof. E is Mg, Ca, Sr, Ba, Zn or a combination thereof. A composite fluoride phosphor having a coordination number of 6 at the coordination center is preferred. Details of such a red phosphor are described, for example, in JP-A-2015-84327. The description of the publication is incorporated herein by reference in its entirety.

Green phosphors include, for example, compounds containing as a main component a solid solution of sialon having a β-Si ₃ N ₄ crystal structure. Preferably, a treatment is performed to reduce the amount of oxygen contained in such sialon crystals to a specific amount (for example, 0.8% by mass) or less. By performing such treatment, a green phosphor that emits sharp light with a narrow peak width can be obtained. Details of such a green phosphor are described, for example, in JP-A-2013-28814. The description of the publication is incorporated herein by reference in its entirety.

The thickness of the wavelength conversion layer is preferably 5 μm to 100 μm, more preferably 30 μm to 50 μm. If the thickness of the wavelength conversion layer is within such a range, the conversion efficiency and durability can be excellent.

As described above, in one embodiment, the wavelength conversion layers are separated by partition walls (light shielding layers). The width of the partition (that is, the distance between adjacent wavelength conversion layers) is preferably 0.1 μm to 100 μm, more preferably 1 μm to 50 μm. In the present invention, it is possible to sufficiently suppress color mixture even if the width of the partition wall is narrow. By narrowing the width of the barrier ribs, a micro LED display device with excellent luminous efficiency can be obtained.

As described above, when configuring a sub-pixel that uses the light from the micro LED as it is (for example, when forming a blue sub-pixel with a blue LED), the wavelength conversion layer can be replaced with a light diffusion layer at that location. . The light scattering layer preferably contains light scattering particles. Materials constituting the light-scattering particles include, for example, alumina, zirconium oxide, titanium oxide, and barium sulfate.

In one embodiment, the micro LED display device further comprises a color filter disposed on the opposite side of the wavelength converting layer (and/or light diffusing layer) to the low refractive index layer. The color filter may have any suitable configuration depending on the color development of sub-pixels. In one embodiment, each sub-pixel is provided with a color filter that cuts out colors other than the desired color. For example, a color filter that cuts blue color development is used in red sub-pixels and green sub-pixels.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

[Example 1]
The configuration shown in FIG. 2(a), that is, a red phosphor and a green phosphor as a wavelength conversion layer are arranged, a low refractive index layer (refractive index: 1.20) and a sealing portion (refractive index: 1.20) are formed. 50), the brightness of red light emission and the brightness of green light emission were determined by optical simulation for a configuration in which a blue LED was arranged directly under a green phosphor. Each wavelength conversion layer has a matrix portion (refractive index 1.47) added with 10% by weight of wavelength converting particles (refractive index 1.80). All of the wavelength conversion layers have a refractive index of 1.50.
The optical properties in this example, and examples and comparative examples described later were calculated using Synopsys optical simulation software (Lighttools). The optical model used for the simulation is as follows.
Each RGB wavelength conversion layer has a thickness of 100 μm and a width of 100 μm. The width of the partition arranged between each RGB was set to 50 nm. An LED was arranged at a position facing each wavelength conversion layer. In this simulation, for the purpose of investigating the effect of color mixture, only the LED corresponding to the green wavelength conversion layer was arranged, and a sealing portion (adhesive layer) was arranged between the LED and the wavelength conversion layer. Table 1 shows the thickness of the sealing portion between the LED and the wavelength conversion layer. The thickness of the low refractive index layer was set to 1.0 μm. Also, the dimensions are assumed to be 78 inches with 4K resolution (3840x2160). A partition wall was arranged between the wavelength conversion layers with a thickness of 50.0 μm, and the transmittance was set to 0%. Also, a light receiver was arranged on each pixel.

[Comparative Example 1]
The configuration shown in FIG. 2(b), that is, a red phosphor and a green phosphor as a wavelength conversion layer are arranged, and directly under the green phosphor via a sealing portion (without a low refractive index layer) For a configuration in which blue LEDs are arranged, the brightness of red light emission and the brightness of green light emission were determined by optical simulation.

<Evaluation>
Table 1 shows the ratio of the luminance in Example 1 to the luminance in Comparative Example 1 (100%). The thickness of the sealing portion between the LED and the wavelength conversion layer was set to 25 μm, 75 μm, and 125 μm, and the luminance ratio was determined for each thickness setting.
In the above configuration, the green phosphor and the blue LED constitute a green-emitting sub-pixel, so that there is a relationship of green emission luminance>red emission luminance, and there is a difference in luminance between green emission and red emission. The larger the value of , the greater the effect of suppressing color mixing.
As is clear from Table 1, in the present invention, by arranging the low refractive index layer, unnecessary red light emission is suppressed and color mixture is preferably suppressed. Moreover, such an effect becomes remarkable by appropriately setting the thickness of the sealing portion between the LED and the wavelength conversion layer.

[Example 2]
The configuration shown in FIG. 2( a ), that is, the red phosphor and the green phosphor as the wavelength conversion layer are arranged, and the low refractive index layer and the sealing portion (thickness between the LED and the wavelength conversion layer: 75 μm) A structure in which a blue LED is arranged directly below the green phosphor through the structure (the thickness of the wavelength conversion layer is 100 μm, the width is 100 μm, the thickness of the partition wall is 50 μm, and the thickness of the low refractive index layer is 1.5 μm). 0 μm), the brightness of red emission and the brightness of green emission were determined by optical simulation.

[Comparative Example 2]
The configuration shown in FIG. 2(b), that is, a red phosphor and a green phosphor as a wavelength conversion layer are arranged, and a green The brightness of red light emission and the brightness of green light emission were determined by optical simulation for a configuration in which a blue LED was arranged directly under the phosphor.

<Evaluation>
Table 2 shows the ratio of the luminance in Example 2 to the luminance in Comparative Example 2 (100%). The refractive index of the low refractive index layer was set to 1.10, 1.20, 1.25, and 1.30, and the above luminance ratio was determined for each refractive index setting.
As is clear from Table 2, in the present invention, by arranging the low refractive index layer, unnecessary red light emission is suppressed and color mixture is preferably suppressed.

10 micro LED array substrate 11 micro LED
REFERENCE SIGNS LIST 12 drive substrate 20 sealing portion 30 low refractive index layer 40 wavelength conversion layer 100 micro LED display device

Claims (7)

a micro LED array substrate including a plurality of micro LEDs;
a sealing portion that seals the plurality of micro LEDs;
a low refractive index layer;
A plurality of wavelength conversion layers formed in sections, provided in this order from the micro LED array substrate side,
Each of the wavelength conversion layers is formed so as to be paired correspondingly with one of the micro LEDs in the thickness direction,
The refractive index of the low refractive index layer is lower than the refractive index of the sealing portion and the refractive index of the wavelength conversion layer,
the difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is 0.10 or more;
The difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is 0.10 or more.
Micro LED display device. 2. The Micro LED display device of claim 1, wherein the refractive index of said low refractive index layer is 1.25 or less. 3. The micro LED display device according to claim 1, wherein the low refractive index layer is a void layer made of a porous body composed of chemically bonded fine particles. 4. The micro LED display device according to any one of claims 1 to 3, wherein the encapsulant is made of adhesive. 5. The micro-LED display device of any of claims 1-4, wherein the individual wavelength converting layers are spaced apart by partition walls. 6. The micro-LED display device according to any of claims 1-5, wherein said micro-LEDs are blue LEDs or ultraviolet LEDs. 7. The micro LED display device according to any one of claims 1 to 6, further comprising a color filter disposed on the opposite side of said wavelength converting layer from said low refractive index layer.

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